Topics In This Section
1. Introduction
2. General Rules of Frying
3. Temperature Control
4. Preparation of Food
5. Fat Absorption and Topping Up
6. Choice of Frying Medium
7. The Spoilage of Fats and Oils
8. Cleaning
9. Frying Specific Foods
10. Recommended Frying Temperatures
11. The Basic Chemistry of Fats and Oils
12. The Chemistry of Fat Spoilage
13. The Visible Effects of Chemical Spoilage
14. The Role of the Oil Refiner
15. The Role of the Fryer
16. Fire Hazards
Reproduced with permission from Pura Food Products Limited
11 The Basic Chemistry of Fats and Oils
Fats and oils are obtained from a wide variety of sources and each one has its own individual properties. They are, however, all of the same chemical type.
The basis of a fat is a substance called glycerol - the same material as the glycerine which can be obtained at a chemist's - which has a chemical formula which
can be illustrated by the shape shown below left:
Each of the 'arms' of this shape can combine with another substance known as a fatty acid, to build up a molecule rather like the diagram below.
Because of the way in which its composition is built up, the chemical substance having this form is known as a triglyceride, and all fats and oils are made up of a
mixture of these triglycerides. A number of different fatty acids exist and to a large extent the character of a particular oil or fat (and its frying properties)
is dictated by the actual fatty acids which are present in the individual triglyceride molecules. Some of these component fatty acids are longer or shorter than
others and they can all combine with a glycerol 'arm'.
There's another complication. Some of these fatty acids possess what could be called a point of weakness (a chemist would call it a double or triple bond) in the molecule.
The reason for this is bound up with the chemistry of the molecule and its presence tends to make that particular material more sensitive and more unstable. To make matters
worse, some fatty acids can have two of these points of weakness and some have three. The more there are, the more unstable the material is likely to be.
Finally, it is possible to have these points of weakness in different places. In the case of a fatty acid with two points of weakness, they can be sited to each other
or far from each other. The closer they are together, the more unstable the resulting molecule will be.
From these descriptions, it can be seen that there can be hundreds of ways in which a triglyceride molecule may be built up. A particular fat is a mixture of many of
these different triglycerides. The properties of, say, lard., are dictated to a large extent by the types of fatty acid which are present. Groundnut oil is also a
mixture but the basic substances, though belonging to the same family, are slightly different and are present in different proportions.